The Buddhist concept muditā, which was translated as appreciative joy or sympathetic joy in English, refers to feeling happy for others in success or happiness. The Appreciative Joy Scale (AJS) was developed to provide a trait-like measurement for appreciative joy in daily life. The AJS consists of three factors: sense of joy, which captures the feeling of joy for others; positive interpersonal bias, which reflects an appreciation or valuing of others’ virtues; and self-transcendence, which mentions the ability to feel appreciative joy in one’s own inferior situation and reflects an unenvious attitude. The initial development study reported that AJS had good reliability and validity, and AJS predicted subjective well-being and lack of envy after controlling relevant concepts. Further studies supported that the appreciative joy measured by AJS differs from positive empathy, that the factors of AJS showed distinguishable function in predicting acceptance of unfair offers in an Ultimatum Game, and that AJS could predict interpersonal perception. Average AJS scores increased after training based on appreciative joy meditation, although the scale might not be sensitive to change. The original AJS developed in Chinese was later translated into English, and the targets of appreciative joy were also extended from friends in the original AJS to other targets in later studies by replacing corresponding words. In sum, preliminary studies showed that the AJS could be a useful tool to measure the concept of appreciative joy and its implications.